1. Field of the Invention
The present invention relates to a method for reducing noise in a read channel of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided up into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
The data written onto the disks has a waveform with numerous transitions. When reading, the waveform is equalized into a partial-response target. The equalized samples are fed into a Viterbi detector to decode the waveform into digital bit strings. Most disk drives contain an error correction code algorithm that detect and compensate for any errors in the data.
FIG. 1 is a schematic showing a conventional partial response maximum likelihood (“PRML”) channel that is used to process data read from a disk. The PRML channel can be categorized into two basic blocks, a signal processing block 2, and a Viterbi detector 4. The signal processing block receives a continuous analog signal y(t) and creates an equalized digitized version of the signal depicted as y1, y2, . . . yN. The Viterbi detector provides a maximum likelihood detection to produce digital samples x1, x2, . . . xN. The digital bits y1, y2, . . . yN can be corrupted by channel noise that may generate detection errors to the Viterbi detector. Normally, the mean of channel noise is zero or close to zero. It would be desirable to utilize this property to reduce noise by performing averages on the samples.